Does Libet disprove free will?
What does early brain activity tell us about conscious choice?
I
Conscious will is an illusion
The brain initiates actions unconsciously. The feeling of deciding comes afterward and does not cause the action.
- Best argument
- The timing data appear to show that the causal process leading to action is well under way before awareness of a decision. Daniel Wegner argued in The Illusion of Conscious Will (2002) that the experience of willing is the mind's interpretation of its own behaviour, not its cause. This fits other findings in which people confidently claim authorship of actions they did not cause, or deny authorship of ones they did.
- Strongest objection
- The interpretation rests on contested assumptions: that the readiness potential reflects a decision, that people can accurately time their awareness against a moving clock, and that flicking a wrist at a random moment tells us anything about real choices.
- Defended by
- Daniel Wegner, Sam Harris
II
Libet's own view: free won't
The brain may initiate actions unconsciously, but consciousness can still veto them in the final fraction of a second.
- Best argument
- Libet himself did not conclude that free will was an illusion. He noted that there was a window of about 150 milliseconds between conscious awareness and movement, during which a person could still cancel the action. Free will might operate as a free won't: we may not choose our impulses, but we choose which to act on.
- Strongest objection
- If the initiation of actions is unconscious, why would the veto be any different? A decision to veto might itself be preceded by unconscious brain activity.
- The reply
- Later experiments by Matthias Schultze-Kraft and colleagues (2016) found that people could cancel a movement after the readiness potential had begun, up to a 'point of no return' about 200 milliseconds before movement, which gives some support to the idea of a late veto.
- Defended by
- Benjamin Libet
III
The readiness potential is not a decision
The readiness potential reflects random background fluctuations in brain activity, not an unconscious decision. The experiments do not show what they seem to.
- Best argument
- In 2012 Aaron Schurger and colleagues showed that the readiness potential can be modelled as neural noise drifting toward a threshold. When it happens to cross the threshold, the movement is triggered. Averaging many trials backward from the movement creates the appearance of a build-up even though no decision was made early. In arbitrary choices with no reason to prefer one moment over another, it is unsurprising that noise tips the balance.
- Strongest objection
- This explains the readiness potential away for arbitrary movements, but leaves open what happens in meaningful decisions, which might involve similar unconscious processes.
- The reply
- Uri Maoz and colleagues (2019) found that the readiness potential was present for arbitrary choices but absent or much weaker for deliberate choices that mattered to the participant, suggesting the original experiments studied the wrong kind of decision.
- Defended by
- Aaron Schurger, Uri Maoz, Alfred Mele
For the full background, variations and open questions, read the entry: Does your brain decide before you do?.